1. Field of the Invention
The present invention relates to a plasma processing apparatus, and more particularly to a plasma reactor chamber having a gas distribution plate (GDP) which is electrically isolated from the electrodes.
2. Description of the Related Art
The requirements for increased device density and greater resolution in semiconductor integrated circuits are continually increasing. A parallel-plate plasma etching process is considered as one of the most widely used processes for semiconductor IC fabrication because it allows for high density and high-resolution patterning of semiconductor substrates.
Such a parallel-plate plasma etching process is performed in a plasma etching apparatus including a vacuum chamber having an upper plate electrode and a lower plate electrode attached to a power supply. The two plate electrodes are parallel and opposed to each other. A semiconductor wafer, which has usually been patterned using conventional photoresist techniques, is placed atop the lower plate electrode. An etching gas is introduced into the chamber, and a high frequency field is generated between the parallel-plate electrodes to generate a plasma from the etching gas. The plasma is driven by the electric field to the surface of the wafer, etching any unmasked areas of the wafer to form the desired pattern thereon.
A conventional plasma etching apparatus is schematically illustrated in FIG. 1. The apparatus includes a vacuum chamber 1. A semiconductor substrate 2 is disposed in the chamber 1. The semiconductor substrate 2 may include a polycrystalline silicon film layer thereon which has been patterned using standard photoresist techniques. The semiconductor substrate 2 is placed on a cathode 4 which serves as a support for the substrate 2, and which is also connected to a high-frequency power supply 3. A top lid 6 is installed at a location opposed to the substrate 2. A GDP 5 is attached to the top lid 6. The GDP 5 includes a plurality of gas nozzles 5a to uniformly introduce a reactive etching gas, for example, a chlorine gas, to the substrate 2. The top lid 6 is connected to ground potential. Accordingly, the GDP 5 is also grounded. The GDP 5 is generally formed from soft anodized aluminum which is produced by coating an aluminum metal with an electrolyzed compound, using conventional sulfuric acid eletrolytic techniques, for example. The GDP 5 is connected to the top lid 6 by screws. The vacuum chamber 1 further includes a gas exhausting device 14 for discharging gas therefrom and a gas inletting device 12 for introducing a reactive etching gas thereinto.
However, there are several disadvantages of the conventional plasma etching apparatus. First, secondary potentials (V.sub.p) are formed in the region beneath the GDP 5 as a result of polymers accumulating in the chamber 1 as schematically shown in FIG. 2. The secondary potentials V.sub.p repeatedly increase until they are periodically discharged by arcing to the GDP 5. The GDP 5 is generally coated with an insulator to a thickness of approximately 0.5 .mu.m. As a result of geometric factors, during the coating process the edges of the gas nozzles of the GDP 5 are only coated to a thickness of 0.3 .mu.m. As a result, the edges of the gas nozzles are more quickly etched by high-frequency power and an etching gas, and the aluminum metal of the quickly etched area is exposed. Afterwards, these exposed "corners" of uninsulated aluminum promote arcing which generates contaminant particles which contaminate the surface of the wafers, resulting in degradation of the wafer quality. Second, the periodic discharge of the secondary potentials causes fluctuations in the state of the plasma itself, which further decreases the uniformity of the surfaces of the wafers.